The present invention relates to a universal mapping tool and to a method for mapping the X, and Y, positions of features positioned on a workpiece, such as a semiconductor device, with respect to each other and with respect to the physical center of the workpiece, and also mapping the elevation positions or Z coordinates of the surface on which such features are positioned.
Semiconductor devices such as semiconductor chips and circuit boards on which such chips are mounted are manufactured to precise standards with respect to the location of features, such as circuitry and circuitry contact points and chip locations. However, minor variations occur in the location of such features due to minor differences in manufacturing processes, such as expansion and contraction differences which may occur in forming such semiconductor devices. Accordingly, it is necessary to accurately map the positions of each such feature, or at least of many such features on each such semiconductor device and to create a data file for each such device which indicates the precise position or coordinates, both vertical (Z) and horizontal (X,Y), in order to later locate such features for testing of circuits and other such features.
One prior art method of mapping such devices involves the use of a mechanical fixturing tool in which an eccentric cam rotates an actuator ring on which two gripping means are slidably mounted equidistant from the precise center (origin) of the workspace. As the actuator ring rotates into the closed position, the two gripping means move equidistantly inwardly toward each other and grasp the corners of a square or rectangular workpiece, thereby placing the physical center of the workpiece directly over the origin. A top gripper plate positions the top surface of the workpiece at a predefined elevation, applying pressure to a linear voltage differential transformer (LVDT) sensor positioned at the center of the work area, which is compressed by the bottom surface of the workpiece to measure the thickness of the work piece.
While such prior art devices accurately map the desired features of a workpiece, they are cumbersome, unduly expensive, and lack sufficient flexibility. One major disadvantage is that they are not sufficiently flexible to adapt to a wide range of workpiece sizes. Thus, it is frequently necessary when changing from one size workpiece to another, to have to shut down and replace the mechanical grippers to ones which are longer or shorter.
The present invention provides an inexpensive and efficient apparatus for automatically mapping workpieces of various sizes and shapes without altering the mechanical fixturing of the apparatus. These advantages are achieved in the present invention by providing a fixed gripping means and a movable gripping means in which the latter is adapted to move toward and away from the fixed gripping means in order to accommodate a wide range of workpiece sizes and shapes. It is a further advantage that the present invention provides means for optically measuring and recording the precise physical center of the workpiece, and other positions relative thereto, including the thickness of the workpiece or an elevation on it, from the relative positions of the fixed and movable gripping means.